Current estimates indicate that 44 million Americans over the age of 50 yrs have osteoporosis or osteopenia. Age-related bone loss results from dysregulated bone metabolism characterized by uncoupling of the catabolic and anabolic activities of osteoclasts and osteoblasts. Despite advances in treatment options over the past two decades, the search continues for more effective, low-cost therapies with fewer side-effects. This search has resulted in the investigation of a number of promising natural compounds and products, including the dried fruit of Prunus domestica L, commonly referred to as dried plum. Among the natural products, dried plum has been shown to have unique anabolic properties by restoring bone lost due to gonadal hormone deficiency and aging. More recently, we have demonstrated the capacity of a crude dried plum extract (DPE) to reverse bone loss in an aging animal model of ovarian hormone deficiency. Given these unique properties, the components in dried plum responsible for the anabolic effects and their mechanisms of action warrant further investigation. Therefore, the purpose of this project is to investigate how different fractions of DPE affect osteogenesis and osteoclastogenesis so that the bioactive components responsible for the anabolic effects can be characterized. The hypothesis to be tested is that the polyphenolic-rich fraction of the DPE will up-regulate osteoblast differentiation and activity and inhibit osteoclastogenesis simultaneously by up-regulating Runx2 and down-regulating RANKL. To test this hypothesis the following specific aims have been developed: 1) To determine the fractions of DPE with the most significant effect on osteoblast and osteoclast differentiation and activity; and 2) To begin to assess and define the mechanisms by which these fractions alter bone metabolism. These aims will be achieved utilizing a series of in vitro experiments with murine and human cell lines and primary cultures. While a number of natural products have been reported to have anti-resorptive activity that prevents bone degradation, few if any have been able to restore bone tissue to the degree observed with dried plum. The results of these studies will significantly advance our understanding of the bioactive components responsible for dried plum's novel effects on bone and provide insight into the underlying mechanisms. Consequently, these results have the potential to accelerate the translation of this work to the clinical setting which is in line with our long-term goal of developing more effective therapeutic strategies for the treatment of osteoporosis.